Happy birthday to YouTube. To get an idea of just how big the video sharing site has become in the seven years since its launch, consider this: users are now uploading 72 hours of video to YouTube per minute. That's a 50 percent gain from a year ago, when users were uploading a meager 48 hours of footage a minute. On the consumption side, YouTube now serves over 3 billion hours of video to 800 million unique users a month, or about 15 minutes per user. What's really remarkable is that YouTube's growth is actually accelerating: while the hours per minute figure increased 25 percent in the eight months leading up to January, it's grown by another 20 percent in the five months since then.